The present invention is particularly addressed toward the processing of superalloy metal powders. Such powders have been used lately to fabricate structures useful at elevated temperatures, in particular, the parts of gas turbine engines. It is quite common that such parts are made by consolidating the powders by hot isostatic pressing. After such pressing, parts are often heat treated to change their metallurgical structures and develop the optimum properties desired.
To obtain the best properties, superalloy powders are atomized and processed under the inert atmosphere. This avoids contamination and unwanted surface films. But small quantities of gas and other volatiles can tend to become adsorbed by, or otherwise occluded with, the metal powders. Thus it has been found prudent to heat powders under vacuum to drive off such contaminants prior to the hot isostatic pressing step. This processing, often called baking or degassing, has been carried out in devices constructed for the purpose. For example, powder has been passed across a sloped and heated plate within a vacuum chamber. Commonly owned U.S. patent application No. 233,726 of Dizek et al, filed Feb. 12, 1981 describes such a process.
The blending step which is used to assure homogenity within a large lot of powder has usually been conducted prior to the baking step. But, it is desirable that powders be processed as few times as possible because non-volatile contaminants can be introduced at each processing step. Thus, in the making of the present invention it has been sought to combine the blending and baking steps. Simply heating the blender shell may appear to be an obvious step. For example, U.S. Pat. No. 2,628,080 of Mack shows a jacketed or double wall blender while U.S. Pat. No. 2,838,392 of Bielawski shows the inner wall of a blender lined with strip heaters. But, for typical superalloy powders the best results are obtained by heating to the vicinity of 700.degree. F. At such temperatures most elastomer seal materials will not be durable and operating a blender at such temperatures presents sealing problems. If special high temperature seals are applied to the blender construction, advantages in ease of use, cost and durability are usually encountered.